The recovery of heat from high-temperature exhaust gases is known. For example in waste incinerators heat from off-gases is used to make steam, and the steam is then used to drive a single stage steam turbine. The turbine shaft power output is then used to generate electricity. The energy conversion efficiency of such a system is relatively low, e.g. about 30%. It is possible to increase the efficiency of such a system by using the low-pressure steam, which exits from the high-pressure turbine, to drive a low-pressure turbine and thus capture more useful work from the steam. However, such low pressure turbines are relatively large and expensive. In addition, turbine blades in the low pressure turbine erode at unacceptable rates, unless expensive reheat equipment is added.
There is a need to improve the efficiency of recovery of useful work obtainable from the heat in exhaust gases of waste incinerators and the like. In the case where the recovery system is used to generate electricity, an advantage of improving efficiency is the lowering of operating costs per kilowatt-hour of energy produced. A further advantage is that the additional electrical energy obtained reduces by a corresponding amount the quantity of fossil fuel that would otherwise have been burned to produce a similar amount of electrical energy. Thus, there is less fossil fuel depletion, less air pollutant production and less global warming due to carbon dioxide production.
The present invention is directed to improving the efficiency of the recovery of heat and of the conversion of heat to useful work, using a binary cycle.